On those occasions when the Copper's instructions do not suffice, you can interrupt the 680x0 and use its instruction set instead. The 680x0 can poll for interrupt flags set in the INTREQ register by various devices. To interrupt the 680x0, use the Copper MOVE instruction to store a 1 into the following bits of INTREQ : Table 2-1: Interrupting the 680x0 Bit Number Name Function ---------- ---- -------- 15 SET/CLR Set/Clear control bit. Determines if bits written with a 1 get set or cleared. 4 COPEN Coprocessor interrupting 680x0. See Chapter 7, "System Control Hardware," for more information about interrupts .